(a) Field of the Invention
The present invention generally relates to a synchronization channel. More particularly, the present invention generally relates to a synchronization channel for a direct communication between terminals.
(b) Description of the Related Art
A wireless access system uses a division duplex for a bi-directional communication. In general, a time division duplex (TDD) for dividing time resources to form an uplink and a downlink and a frequency division duplex (FDD) for dividing frequency resources to form the uplink and the downlink are used. The TDD needs a transition time gap (TTG) when a transmitting operation and a receiving operation are switched.
Recently, a direct communication between terminals is developed for a reliable wireless communication in degraded network conditions. For example, IEEE 802.16n or IEEE 802.16.1a standard group is working on this research. The direct communication uses some of infra communication resources, and a voice/video communication and data transmission/reception between the terminals can be performed in the infra communication system and green field condition where the infra communication system is destroyed. A distributed synchronization scheme is used for synchronization of a direct communication terminal, and some of the direct communication resources are used to transmit a synchronization channel for the distributed synchronization.
In the direct communication, the terminal can receive data through a dedicated channel after transmitting the synchronization channel, and can transmit data through the dedicated channel after receiving the synchronization channel. In this case, a transmitting/receiving (Tx/Rx) transition time is required between the synchronization channel and the dedicated channel. However, when the Tx/Rx transition time is inserted in a synchronization channel structure of a conventional direct communication, the terminal cannot transmit some data of the synchronization channel message part. In this case, because the terminal should increase a code rate of the message part to transmit all data, reliability of the message can be deteriorated. Further, if a fixed Tx/Rx transition time is inserted although some terminals require the Tx/Rx transition time, resource efficiency is decreased.